As is exemplified by U.S. Pat. No. 76,472 to Kohl, issued in 1868, it has long been known that three-dimensional images occur if identical images are placed adjacent one another and viewed through a pair of lenses optically shielded from one another so that the viewer's eyes function independently of one another. The stereoscope disclosed in the Kohl patent includes a plurality of pictures stacked therein for viewing. Patents such as U.S. Pat. No. 669,604 to Twifford and U.S. Pat. No. 670,752 to Wyatt, both issued in 1901, also disclose a plurality of pictures for stereoscopic viewing; however, instead of being stacked, the pictures are mounted on a rotatable drum. The rotatable drum concept is further seen in patents such as U.S. Pat. No. 739,402 to Eastman, issued in 1903, and U.S. Pat. No. 764,136 to Leeland, issued in 1904. Development of stereoscopic viewers with multiple pictures or images has continued and, as late as 1979, patents have issued on such devices as is exemplified by U.S. Pat. Nos. 4,146,303 to Baba and 4,158,480 to Mitchell.
None of these prior art approaches allow one to conveniently view photoprints which are stored in albums or binders in way that the photoprints are readily viewable either with or without a stereoscope.